GUNTERITE, Na4(H2O)16(H2V10O28){middle dot}6H2O, A NEW MINERAL SPECIES WITH A DOUBLY-PROTONATED DECAVANADATE POLYANION: CRYSTAL STRUCTURE AND DESCRIPTIVE MINERALOGY

Abstract

Gunterite, Na 4 (H 2 O) 16 (H 2 V 10 O 28 )•6H 2 O, is a new mineral species from the West Sunday mine, Slick Rock district, San Miguel County, Colorado, U.S.A. Crystals of gunterite are tabular on {001} and generally stacked into elongate curved multiple crystals up to 0.5 mm in maximum dimension; the crystals are orange-yellow, with a yellow streak. The mineral displays a subadamantine luster, and is transparent; it does not fluoresce in short-or long-range ultraviolet radiation. Gunterite has a hardness of about 1, a brittle tenacity, and an irregular fracture; no cleavage or parting was observed. The density calculated from the empirical formula using the single-crystal cell data is 2.398 g cm -3 . Gunterite is biaxial (+), with a 1.735(5), b 1.770(5) and g 1.825(5); 2V is equal to 78° (white light). The dispersion v < r is strong and parallel. Optical orientation;is soluble in water at room temperature. Electronprobe microanalysis and the crystal-structure solution provided the empirical formula (V + Al = 10 apfu): (Na 3.20 K 0.02 Ca 0.87 ) S4.09 [H 1.06 (V 9.99 Al 0.01 ) S10 O 28 ]•22H 2 O. The simplified formula of gunterite is Na 4 (H 2 O) 16 (H 2 V 10 O 28 )•6H 2 O. There is extensive substitution of Ca for Na in gunterite, yielding a structural formula of (Na 4-x Ca x ) S4.00 (H 2 O) 16 (H 2-x V 10 O 28 )•6H 2 O; the average value of x from the chemical analyses is 0.85. Gunterite is monoclinic, C2/m, with a 19.848(2), b 10.1889(11), c 13.1184(15) Å, b 130.187(9)°, V 2026.6(4) Å 3 , and Z = 2. The strongest four lines in the diffraction pattern [d in Å(I)hkl] are: 10.01(100)201,001, 8.44(72)110, 8.09(46)111, and 2.997(29)331,401. The atomic arrangement of gunterite was refined to R 1 = 0.0632. The structural unit is a doubly-protonated decavanadate polyanion, {H 2 [V 10 O 28 ]}. The interstitial units linking the structural units contain two Na polyhedra; the Na2 polyhedron is split into two partially occupied sites that are 0.76 Å apart, and significant Ca occupies that site. Several of the H 2 O molecules in the interstitial complex are disordered. The mineral is named in honor of Mickey E. Gunter, Professor of Mineralogy at the University of Idaho. SoMMAiRELa gunterite, Na 4 (H 2 O) 16 (H 2 V 10 O 28 )•6H 2 O, est une nouvelle espèce minérale provenant de la mine West Sunday mine, district de Slick Rock, comté de San Miguel, au Colorado. Les cristaux sont tabulaires sur {001} et généralement empilés en amas de cristaux courbes allongés atteignant 0.5 mm en dimension maximale; les cristaux sont orange-jaunes, avec une rayure jaune. Il s'agit d'un minéral transparent ayant un éclat subadamantin, qui ne montre aucune fluorescence en lumière ultraviolette, en longueur d'onde courte ou longue. La gunterite possède une dureté d'environ 1, une ténacité cassante, et une §

A Versatile Polyoxovanadate in Diverse Cation Matrices: A Supramolecular Perspective

“…These sodium-water chains are laterally linked by the decavanadate anions to form a two-dimensional coordination polymeric structure; [Co(H 2 O) 6 ] 2+ remains as an isolated discrete coordination complex cation located in the void space (Figure 3) to counterbalance the negative charges of the decavanadate anion. In the language of decavanadate mineral crystallography, these cations (e.g., sodium and cobalt ions in compound 1 ) are called interstitial units (Hughes et al, 2002, 2005, 2008; Colombo et al, 2011; Kampf et al, 2011b, 2013b, 2014). For example, in the crystal structure of the kokinosite mineral (Kampf et al, 2014), the interstitial unit has a composition of (Na 2 Ca 2 •24H 2 O) 6+ and the decavanadate anion (V 10 O 28 ) 6− forms the structural unit of the mineral.…”

“…In 2011, Kampf et al reported diprotonated decavanadate based mineral, gunterite Na 4 (H 2 V 10 O 28 ) •22H 2 O (Kampf et al, 2011b). In both the crystal structures, the proton on the decavanadate anion could not be located, but formulated from elemental analyses and crystallographic investigation on the cationic part.…”

“…In the crystal structure of compound 2 , a sodium trimer-water cluster [Na 3 (H 2 O) 14 ] 3+ per formula unit is characterized, which unlike compound 1 is not coordinated to decavanadate anion. But in the case of the gunterite mineral, the sodium water cluster is coordinated to the polyanion (Kampf et al, 2011b). In the crystal structure of synthesized compound 2 , the [Zn(H 2 O) 6 ] 2+ moiety remains as an isolated discrete coordination complex cation, counter balancing the residual charge of the decavanadate anion.…”

One-dimensional decavanadate chains in the crystal structure of Rb4[Na(H2O)6][HV10O28]·4H2O

“…K + and Ba 2+ , or Na + and Ca 2+ , or atoms of the 'large' rare-earth elements. Occasionally, decavanadate structures are described by higher symmetry monoclinic space groups, namely P2/c (P2/n; two isotypic varieties with large Rb or K atoms and Na atoms, including our structure), C2/c [two synthetic phases: Sr 3 (V 10 O 28 )(H 2 O) 22 (Nieto et al, 1993) and Na 4 K 2 (V 10 O 28 )(H 2 O) 18 (Lee, 2006), the mineral lasalite, Na 2 Mg 2 (V 10 O 28 )(H 2 O) 20 (Hughes et al, 2008) and its synthetic analogue (Iida & Ozeki, 2004)], and C2/m [the Ca mineral pascoite (Hughes et al, 2005) and its partly substituted Mg variety (Kampf & Steele, 2008), and the Na mineral gunterite (Kampf, Hughes, Marty & Nash, 2011)]. Only three orthorhombic decavanadates with inorganic cations exist, to our knowledge, and all three are formed by relatively small metal atoms, viz.…”

“…Only a few examples of protonated decavanadates with inorganic cations have been reported. In addition to the mineral rakovanite, Na 3 (H 3 V 10 O 28 )(H 2 O) 15 (space group P2 1 /c; Kampf, Hughes, Marty & Gunter, 2011), its synthetic analogue (Duraisamy et al, 2000) and the mineral gunterite, Na 4 (H 2 V 10 O 28 )(H 2 O) 22 (space group C2/m; Kampf, Hughes, Marty & Nash, 2011), there are two isotypic phases, i.e. NaRb 4 (HV 10 O 28 )(H 2 O) 10 and NaK 4 (HV 10 O 28 )(H 2 O) 10 (space group P2/c), and Cs 4 (H 2 V 10 O 28 )(H 2 O) 4 (space group P2 1 /c) (Tat'yanina et al, 1987).…”